We plan to build a flow cell in which the partial pressure of oxygen can be varied rapidly in order to study sickling under conditions that more resemble physiological conditions than have been used in the past. Since there is a broad distribution in the cellular hemoglobin concentration, a large number of cells need to be analyzed simultaneously. The change in shape of the cells in the flow cell will be observed under a microscope. A video camera will transmit the picture to a computer, where the fraction of cells that have sickled will be automatically determined using image analysis algorithms.